RE: [Patch v2 03/15] CIFS: Use offset when reading pages

[Long Li <longli@microsoft.com>]

> From: Tom Talpey <tom@talpey.com>
> Sent: Saturday, June 23, 2018 6:59 PM
> To: Long Li <longli@microsoft.com>; Steve French <sfrench@samba.org>;
> linux-cifs@vger.kernel.org; samba-technical@lists.samba.org; linux-
> kernel@vger.kernel.org; linux-rdma@vger.kernel.org
> Subject: Re: [Patch v2 03/15] CIFS: Use offset when reading pages
> 
> On 5/30/2018 3:47 PM, Long Li wrote:
> > From: Long Li <longli@microsoft.com>
> >
> > With offset defined in rdata, transport functions need to look at this
> > offset when reading data into the correct places in pages.
> >
> > Signed-off-by: Long Li <longli@microsoft.com>
> > ---
> >   fs/cifs/cifsproto.h |  4 +++-
> >   fs/cifs/connect.c   |  5 +++--
> >   fs/cifs/file.c      | 52 +++++++++++++++++++++++++++++++++++++--------
> -------
> >   fs/cifs/smb2ops.c   |  2 +-
> >   fs/cifs/smb2pdu.c   |  1 +
> >   5 files changed, 45 insertions(+), 19 deletions(-)
> >
> > diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h index
> > dc80f84..1f27d8e 100644
> > --- a/fs/cifs/cifsproto.h
> > +++ b/fs/cifs/cifsproto.h
> > @@ -203,7 +203,9 @@ extern void dequeue_mid(struct mid_q_entry *mid,
> bool malformed);
> >   extern int cifs_read_from_socket(struct TCP_Server_Info *server, char
> *buf,
> >   			         unsigned int to_read);
> >   extern int cifs_read_page_from_socket(struct TCP_Server_Info *server,
> > -				      struct page *page, unsigned int to_read);
> > +					struct page *page,
> > +					unsigned int page_offset,
> > +					unsigned int to_read);
> >   extern int cifs_setup_cifs_sb(struct smb_vol *pvolume_info,
> >   			       struct cifs_sb_info *cifs_sb);
> >   extern int cifs_match_super(struct super_block *, void *); diff
> > --git a/fs/cifs/connect.c b/fs/cifs/connect.c index 83b0234..8501da0
> > 100644
> > --- a/fs/cifs/connect.c
> > +++ b/fs/cifs/connect.c
> > @@ -594,10 +594,11 @@ cifs_read_from_socket(struct TCP_Server_Info
> > *server, char *buf,
> >
> >   int
> >   cifs_read_page_from_socket(struct TCP_Server_Info *server, struct page
> *page,
> > -		      unsigned int to_read)
> > +	unsigned int page_offset, unsigned int to_read)
> >   {
> >   	struct msghdr smb_msg;
> > -	struct bio_vec bv = {.bv_page = page, .bv_len = to_read};
> > +	struct bio_vec bv = {
> > +		.bv_page = page, .bv_len = to_read, .bv_offset =
> page_offset};
> >   	iov_iter_bvec(&smb_msg.msg_iter, READ | ITER_BVEC, &bv, 1,
> to_read);
> >   	return cifs_readv_from_socket(server, &smb_msg);
> >   }
> > diff --git a/fs/cifs/file.c b/fs/cifs/file.c index 1c98293..87eece6
> > 100644
> > --- a/fs/cifs/file.c
> > +++ b/fs/cifs/file.c
> > @@ -3026,12 +3026,20 @@ uncached_fill_pages(struct TCP_Server_Info
> *server,
> >   	int result = 0;
> >   	unsigned int i;
> >   	unsigned int nr_pages = rdata->nr_pages;
> > +	unsigned int page_offset = rdata->page_offset;
> >
> >   	rdata->got_bytes = 0;
> >   	rdata->tailsz = PAGE_SIZE;
> >   	for (i = 0; i < nr_pages; i++) {
> >   		struct page *page = rdata->pages[i];
> >   		size_t n;
> > +		unsigned int segment_size = rdata->pagesz;
> > +
> > +		if (i == 0)
> > +			segment_size -= page_offset;
> > +		else
> > +			page_offset = 0;
> > +
> >
> >   		if (len <= 0) {
> >   			/* no need to hold page hostage */ @@ -3040,24
> +3048,25 @@
> > uncached_fill_pages(struct TCP_Server_Info *server,
> >   			put_page(page);
> >   			continue;
> >   		}
> > +
> >   		n = len;
> > -		if (len >= PAGE_SIZE) {
> > +		if (len >= segment_size)
> >   			/* enough data to fill the page */
> > -			n = PAGE_SIZE;
> > -			len -= n;
> > -		} else {
> > -			zero_user(page, len, PAGE_SIZE - len);
> > +			n = segment_size;
> > +		else
> >   			rdata->tailsz = len;
> > -			len = 0;
> > -		}
> > +		len -= n;
> > +
> >   		if (iter)
> > -			result = copy_page_from_iter(page, 0, n, iter);
> > +			result = copy_page_from_iter(
> > +					page, page_offset, n, iter);
> >   #ifdef CONFIG_CIFS_SMB_DIRECT
> >   		else if (rdata->mr)
> >   			result = n;
> >   #endif
> 
> I hadn't noticed this type of xonditional code before. It's kind of ugly to
> modify the data handling code like this. Do you plan to break this out into an
> smbdirect-specific hander, like the cases above and below?

This is a good point. I will look for ways to improve this.

> 
> >   		else
> > -			result = cifs_read_page_from_socket(server, page,
> n);
> > +			result = cifs_read_page_from_socket(
> > +					server, page, page_offset, n);
> >   		if (result < 0)
> >   			break;
> >
> > @@ -3130,6 +3139,7 @@ cifs_send_async_read(loff_t offset, size_t len,
> struct cifsFileInfo *open_file,
> >   		rdata->bytes = cur_len;
> >   		rdata->pid = pid;
> >   		rdata->pagesz = PAGE_SIZE;
> > +		rdata->tailsz = PAGE_SIZE;
> >   		rdata->read_into_pages = cifs_uncached_read_into_pages;
> >   		rdata->copy_into_pages = cifs_uncached_copy_into_pages;
> >   		rdata->credits = credits;
> > @@ -3574,6 +3584,7 @@ readpages_fill_pages(struct TCP_Server_Info
> *server,
> >   	u64 eof;
> >   	pgoff_t eof_index;
> >   	unsigned int nr_pages = rdata->nr_pages;
> > +	unsigned int page_offset = rdata->page_offset;
> >
> >   	/* determine the eof that the server (probably) has */
> >   	eof = CIFS_I(rdata->mapping->host)->server_eof;
> > @@ -3584,13 +3595,21 @@ readpages_fill_pages(struct TCP_Server_Info
> *server,
> >   	rdata->tailsz = PAGE_SIZE;
> >   	for (i = 0; i < nr_pages; i++) {
> >   		struct page *page = rdata->pages[i];
> > -		size_t n = PAGE_SIZE;
> > +		unsigned int to_read = rdata->pagesz;
> > +		size_t n;
> > +
> > +		if (i == 0)
> > +			to_read -= page_offset;
> > +		else
> > +			page_offset = 0;
> > +
> > +		n = to_read;
> >
> > -		if (len >= PAGE_SIZE) {
> > -			len -= PAGE_SIZE;
> > +		if (len >= to_read) {
> > +			len -= to_read;
> >   		} else if (len > 0) {
> >   			/* enough for partial page, fill and zero the rest */
> > -			zero_user(page, len, PAGE_SIZE - len);
> > +			zero_user(page, len + page_offset, to_read - len);
> >   			n = rdata->tailsz = len;
> >   			len = 0;
> >   		} else if (page->index > eof_index) { @@ -3622,13 +3641,15
> @@
> > readpages_fill_pages(struct TCP_Server_Info *server,
> >   		}
> >
> >   		if (iter)
> > -			result = copy_page_from_iter(page, 0, n, iter);
> > +			result = copy_page_from_iter(
> > +					page, page_offset, n, iter);
> >   #ifdef CONFIG_CIFS_SMB_DIRECT
> >   		else if (rdata->mr)
> >   			result = n;
> >   #endif
> 
> Ditto previous comment/question.
> 
> >   		else
> > -			result = cifs_read_page_from_socket(server, page,
> n);
> > +			result = cifs_read_page_from_socket(
> > +					server, page, page_offset, n);
> >   		if (result < 0)
> >   			break;
> >
> > @@ -3807,6 +3828,7 @@ static int cifs_readpages(struct file *file, struct
> address_space *mapping,
> >   		rdata->bytes = bytes;
> >   		rdata->pid = pid;
> >   		rdata->pagesz = PAGE_SIZE;
> > +		rdata->tailsz = PAGE_SIZE;
> >   		rdata->read_into_pages = cifs_readpages_read_into_pages;
> >   		rdata->copy_into_pages = cifs_readpages_copy_into_pages;
> >   		rdata->credits = credits;
> > diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c index
> > 7c0edd2..1fa1c29 100644
> > --- a/fs/cifs/smb2ops.c
> > +++ b/fs/cifs/smb2ops.c
> > @@ -2467,7 +2467,7 @@ read_data_into_pages(struct TCP_Server_Info
> *server, struct page **pages,
> >   			zero_user(page, len, PAGE_SIZE - len);
> >   			len = 0;
> >   		}
> > -		length = cifs_read_page_from_socket(server, page, n);
> > +		length = cifs_read_page_from_socket(server, page, 0, n);
> >   		if (length < 0)
> >   			return length;
> >   		server->total_read += length;
> > diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c index
> > a02f6b6..f603fbe 100644
> > --- a/fs/cifs/smb2pdu.c
> > +++ b/fs/cifs/smb2pdu.c
> > @@ -2683,6 +2683,7 @@ smb2_readv_callback(struct mid_q_entry *mid)
> >   	struct smb_rqst rqst = { .rq_iov = rdata->iov,
> >   				 .rq_nvec = 2,
> >   				 .rq_pages = rdata->pages,
> > +				 .rq_offset = rdata->page_offset,
> >   				 .rq_npages = rdata->nr_pages,
> >   				 .rq_pagesz = rdata->pagesz,
> >   				 .rq_tailsz = rdata->tailsz };
> >